find one or more chars in object name
Ok first try to think what you really want to do. You are trying to select some object based on its name, however you are looking at the selected objects.
So what you really want to do, is unselect everything else (because the object(s) you do want is already selected).

Here is a loop that goes through every selected object bpy.context.selected_objects:, and if the search term does not match the current object name it deselects it. Which leaves you with only the matching objects selected.  

import bpy
searchTerm = "cube"
for obj in bpy.context.selected_objects:
    if searchTerm.lower() not in obj.name.lower():
        obj.select = False


The .lower() part converts everything to lower case, which makes the search case insensitive (if you did not "c" would not match "Cube").



Now one way you could search for more then one search term at a time, is to add in a or into the if statement.
Which would look like this:

if "a" not in obj.name.lower() or " " not in obj.name.lower():


Note the second condition " ", that is searching for a space in the object name.



Here is a slightly more useful version that looks through all the objects,  selects the matching objects and deselects any that do not match.

import bpy

for obj in bpy.data.objects:
    if "s" in obj.name.lower():
        obj.select = True
    else:
        obj.select = False